The invention relates to an improved thrust bearing preferably for extreme service applications partly through the use of a novel bearing cage assembly. Moreover, the invention allows for increased durability and useful life of both the thrust bearing and, when the thrust bearing is in use, a rotating shaft through the thrust bearing.
Thrust bearings are commonly used In equipment with rotating shafts to absorb axial loads on the shafts and are usually comprised of a bearing cage assembly positioned between a dynamic race and a static race. The races are, for the most part, constructed of hardened steel, and the bearing cage assembly is normally constructed of brass, steel or polymer material.
A bearing cage assembly normally consists of a pair of annular cage portions having opposing upper and lower planar surfaces defining circumferentially spaced slots for receiving roller elements. The dimensions of the roller slots are such that radiused portions of the roller elements extend above the upper and lower planar surfaces which are then guided along a radial path when in contact with the race components.
The potential to obtaining maximum bearing capacity of a thrust bearing lies in the number, length and diameter of the roller elements. Generally, as the internal space in a bearing cage is increased to accommodate an increase in number and/or size of the rolling elements, the bearing""s load capacity increases, Therefore, a maximum bearing capacity will be achieved with a bearing cage assembly design that allows for maximum utilization of the internal space which can be occupied by the rolling elements.
There are three equations that may be used to determine the performance of a cylindrical roller thrust bearing. First, the static capacity of a bearing is determined by:
xe2x80x83Coa=32150xc3x97ZLweDwe
Where,
Coa is the basic static load rating in pounds force,
Z is the number of rolling elements,
Lwe is the effective roller length in inches, and
Dwe is the effective roller diameter In inches.
Second, the dynamic capacity of a bearing is determined by:
Ca=fcmLwe7/9Z3/4Dwe29/27
Where,
Ca is the basic dynamic load rating in pounds force
fcm is a factor influenced by the pitch diameter of the rollers,
Lwe is the effective roller length in inches,
Z Is the number of rolling elements, and
Dwe is the effective roller diameter in inches.
Lastly, the basic rating life is determined by:
L10=(Ca/Pa)10/3xc3x97106
where,
L10 is life associated with 90% reliability (in total revolutions),
Ca is the basic dynamic load rating In pounds force,
Pa is the applied load on the bearing in pounds force.
On the basis of the above-noted relationships, it is apparent that by increasing any one or more of the length of the roller elements, the number of the roller elements contained in the bearing cage, and the diameter of the roller elements, the basic static load capacity, the basic dynamic load capacity, and the basic rating life of the bearing substantially increases. For example, increasing the roller length by 10% can result in a 10% increase in static load capacity, an 8% increase in dynamic capacity, and a 37% increase in basic rating life.
Machined bearing cages made from brass or steel require thick cross-sections between the rolling element pockets to keep them sufficiently aligned, Rolling elements are placed in each of the pockets and a ring is secured around the outside diameter to hold the rolling elements in place. Other versions of the two-member steel cages also require thicker side cross-sections to hold the two halves together. This type of design severely limits the size and the quantity of the rolling elements, thus limiting the thrust bearing""s capacity.
On the other hand, injection molded cages of polymer material allow extremely thin cross-sections between the rolling element pockets but still require thick peripheral inside and outside sidewalls of the bearing cage frame in order to secure the two halves together. Thick peripheral sidewalls limit the overall size of the rolling elements which can be accommodated by the bearing cage. Thus, similar to the metal bearing cage described above, bearing cages manufactured from polymer material also have limitations on the amount of load capacity that can be achieved as a result of their design, Moreover, the polymer materials easily degrade in high temperature applications and thus, are not the preferred material from which to manufacture bearing cages.
A common drawback associated with the aforementioned machined cages and injection molded cages is that solid dividers are employed to form roller pockets which severely limits the overall size and quantity of the roller elements contained within the bearing cage. In addition, these dividers provide a place for abrasive particles to become lodged and rub on the rolling elements within the bearing cage assembly, thus potentially reducing the life of the bearing. Although the bearings are immersed in lubricant, the latter has a limited ability to remove abrasive grit out from between the roller elements. Eventually, a build-up of abrasive grit occurs and one or more of the roller elements becomes jammed against the cage or is damaged by the grit thereby reducing the life of a thrust bearing.
To facilitate assembly of the bearing cage assembly with the roller elements, the bearing cages are generally formed of a pair of annular members which mate or interlock along an interface normal to the axis of the bearing cage assembly. In most instances, an interlocking engagement is used to secure the two halves of the bearing cage together after the pair of annular members and the roller elements are properly assembled. For example, in Canadian Patent Application No. 2,292,286, one of the cage members is formed with a radially outwardly projecting circumferential lip, while the other cage member is formed with a radially inwardly projecting circumferential lip adapted to interlock with the outwardly projecting lip to prevent axial separation of the cage members while permitting relative rotational movement thereof.
However, a disadvantage to using this type of engagement profile is that optimal thinness of the sidewall cannot be obtained which could otherwise allow for maximized roller fill (roller fill being the volume occupied by the rollers in the bearing cage) and, subsequently, increased bearing load capacity. There is a current need to increase the roller fill of a thrust bearing as well as to increase the service life of such bearing.
Equipment that is subjected to extreme service applications often experience vibrations that can result in contact between the rotating shaft and the bearing race edges. The inside edges of the bearing races are often quite sharp due to the grinding process used to dress the bearing race surfaces. This contact tends to cut sharp grooves into the rotating shaft. The sharp grooves can act as critical notch stress risers and lead to catastrophic failure of the shaft. There is a current need to reduce the risk of such an occurrence.
According to one aspect of the present invention there is provided a bearing cage assembly component for an axial thrust bearing for a rotating shaft, the component comprising an annular bearing cage frame and a plurality of roller elements, The annular bearing cage frame comprises:
an inside sidewall and an outside sidewall, the inside sidewall having an exterior surface to be adjacent the rotating shaft, the exterior surface having a smoothly curved axial profile for reducing abrasion on the shaft;
a base extending between the respective sidewalls and including a plurality of first roller element slots; and
a top extending between the respective sidewalls and including a plurality of second roller element slots respectively aligned with the first roller element slots thereby providing pairs of aligned roller element slots in the base and top. The plurality of roller elements are respectively spaced from each other around the bearing cage frame at positions between the respective sidewalls. Each of the positions is also between a pair of the aligned roller element slots whereby radiused parts of each of the roller elements protrude through each pair of the aligned roller element slots. Preferably, the smoothly curved axial profile of the exterior surface of said inside sidewall is convex. Further preferably, the smoothly curved axial profile of the exterior surface of the inside sidewall is comprised of a plurality of straight sections joined by smoothly curved sections.
In another aspect, the invention provides a bearing cage assembly component for an axial thrust bearing for a rotating shaft, the component comprising an annular bearing cage frame and a plurality of roller elements, the annular bearing cage frame comprising:
an inside sidewall and an outside sidewall;
a base extending between the respective sidewalls and including a plurality of first roller element slots; and
a top plate extending between the respective sidewalls and including a plurality of second roller element slots respectively aligned with the first roller element slots thereby providing pairs of aligned roller element slots in the base and top plate, the plurality of roller elements being respectively spaced from each other around the bearing cage frame at positions between the respective sidewalls, each of the positions also being between a pair of the aligned roller element slots whereby radiused parts of each of the roller elements protrude through each pair of the aligned roller element slots, and the top plate is secured along an inside perimeter thereof by a crimped top end of the inside sidewall and along an outside perimeter thereof by a crimped top end of the outside sidewall. Preferably, the top plate has a bevelled edge along an upper edge of the inside perimeter such that the crimped top end of the inside sidewall is crimped over the bevelled edge. More preferably, the bevelled edge is at an angle of about 45 degrees to the inside sidewall. The top plate may have a second bevelled edge along an upper edge of the outside perimeter such that the crimped top end of the outside sidewall is crimped over the second bevelled edge. Preferably, the second bevelled edge is at an angle of about 45 degrees to the outside sidewall. The top plate may be supported along a lower edge of the inside perimeter by a ledge around a perimeter of an interior surface of the inside sidewall, and the top plate may also be supported along a lower edge of the outside perimeter by a ledge around a perimeter of an interior surface of the outside sidewall.
In a further aspect, the invention provides a bearing cage assembly component for an axial thrust bearing for a rotating shaft, the component comprising an annular bearing cage frame and a plurality of roller elements, the annular bearing cage frame comprising:
an inside sidewall and an outside sidewall, the inside sidewall having an exterior surface to be adjacent the rotating shaft, the exterior surface having a smoothly curved axial profile for reducing abrasion on the shaft;
a base extending between the respective sidewalls and including a plurality of first roller element slots; and
a top plate extending between the respective sidewalls and Including a plurality of second roller element slots respectively aligned with the first roller element slots thereby providing pairs of aligned roller element slots in the base and top plate, the plurality of roller elements being respectively spaced from each other around the bearing cage frame at positions between the respective sidewalls, each of the positions also being between a pair of the aligned roller element slots whereby radiused parts of each of the roller elements protrude through each pair of the aligned roller element slots; the top plate being secured along an inside perimeter thereof by a crimped top end of the inside sidewall and along an outside perimeter thereof by a crimped top end of the outside sidewall.
The bearing cage assembly forms a strong box-shaped cross-section. Advantageously, one aspect of the design of the bearing cage assembly allows for the utilization of thin sidewalls compared to conventional bearing cages by maximizing the internal space available for containment of the rolling elements. Because more space is available to contain the rolling elements compared to current machined brass or steel versions of a bearing cage, the quantity of the roller elements contained in the bearing cage can be increased. Since a reduction in the thickness of the sidewalls also allows for the length of the roller elements to be increased compared to current polymer versions of the bearing cage, the combination of both these features (i.e. more efficient containment of the roller elements within the internal space of the bearing cage and an increase in the length of the rolling element) ultimately results in a higher capacity thrust bearing. The bearing cage of such configuration also keeps the interior of the bearing cage assembly open, thereby providing better lubrication of the rolling elements because they can be completely surrounded by lubricating grease or oil.
Based on the equations noted above, it was observed that the bearing cage assembly of the present invention was able to increase the dynamic bearing capacity by 44% and the basic rating life by 337% having 13 replacement rollers, each being 15 mm in diameter, 15 mm in length, when compared to a conventional bearing cage assembly having 19 rollers, each being 11 mm In diameter, 11 mm in length. Since the novel design of the bearing cage assembly of the present invention increases the internal space available for containment of the roller elements, an increase in one or more of the number of roller elements, the length of the roller elements and the diameter of the roller elements can be employed. In the foregoing example the number of roller elements actually was decreased, but the increases in roller length and diameter resulted in an overall substantial increase in the load capacity and life of the thrust bearing.
Another aspect of the invention is the utilization of a smoothly curved axial profile on the external surface of the inside circular sidewall of one or more, and optimally all of the components of the thrust bearing (i.e. the dynamic and static bearing races and the bearing cage assembly) which minimizes surface area contact with the rotating shaft and eliminates any sharp edges or corners which could otherwise damage the rotating shaft. One problem solved by the present invention occurs at or near the place of contact between the bearing cage assembly (and race components) and the rotating shaft. More specifically, the locations of contact between the thrust bearing components and the rotating shaft are where the external surfaces of the inside circular sidewalls of the thrust bearing components meet the external surface of the outside circular sidewall of the rotating shaft. When vibrations of the thrust bearing begin to occur under extreme service applications, the presence of any sharp corners or edges on the external surfaces of the circular inside sidewalls of the bearing components have the potential to cut sharp grooves in the rotating shaft. Accordingly, the novel design of the smoothly curved axial profiles of the external surfaces of the circular inside sidewalls of the respective thrust bearing components effectively leads to longer durability and useful life of the shaft. It should be noted that the formation of the smoothly curved axial profile is not limited to a continuous curve, but can be a series of flat surfaces, e.g. a combination of a small flat surface(s), adequately tapered on each side with curves joining them.
Accordingly, it is an object of the invention to provide an improved thrust bearing cage which eliminates the use of dividers between the roller elements and minimizes the thickness of the bearing cage sidewalls thereby maximizing roller element fill and bearing load capacity.
It is a further object of the invention to provide a smooth curved surface on the external face of the circular inside sidewall of the bearing cage and race components to reduce surface area contact with the rotating shaft and prevent damage to the shaft due to the elimination of any sharp edges or corners.